The invention relates to a coupling piece for connecting containers. More particularly, the present invention concerns a coupling device for connecting containers which includes a locking bolt which is rotatable between a locking position and a release position.
By means of such a coupling piece, containers of standardized design can be connected together vertically on top of one another. For this purpose, the containers have corner fittings which conform to international standards and which have orifices in their horizontal surface. Coupling pieces of the type mentioned in the introduction, which are in general also referred to by the term "twistlock", are known, and in these the connecting force (anchoring force) is transmitted solely via the crossbars and the locking bolt.
Another type of known twist lock is referred to as a "permanent-base twistlock" in the specialized jargon. Its housing is equipped, at one end, with a foot which is anchored in the corner fitting of a (lower) container as a result of the rotation of the housing. Here, a crossbar is provided only at the top end of the locking bolt. The bottom end of the bolt is anchored rotatably in the housing or by means of small crossbars or flanges on the lower outer face of the housing. Here, the force is transmitted with the assistance of the housing. The disadvantage of the last-mentioned "permanent-base" type of twistlock is that it has a lower load-bearing capacity. This is because the rotary anchoring of the locking bolt in or on the housing is critical. On the other hand, however, this type also has considerable advantages which is one reason for the increase in use of this type. It must be assumed, here, that very great care is exercised when containers are loaded in harbour. There is no guarantee that the twistlocks are always attached to the corner fittings in one and the same relative position. However, this is a prerequisite for making it possible, by means of the position of the actuating lever (hand lever) for the locking bolt, to ascertain from outside whether the twistlock between the containers is in the locking position or the release position. The twistlocks are designed so that, when assembled properly the right way up, the hand lever always points to the left in the locking position. In a cargo inspection, it is consequently possible to ascertain visually, by checking the relative position of the hand lever, whether the twistlock is locked or not. This inspection is necessarily deficient if the twistlocks are fitted upside-down. This only applies to the type of twistlock mentioned first in the introduction.
This risk does not arise in a twistlock of the "permanent-base" type, because it is only possible to assemble it when the "anchoring foot" of the housing is directed downwards. In particular, for assembly, it is necessary for the housing to be rotated in the orifice in the corner fitting so that the lateral flanges of the foot can engage. In other words, the housing is inserted into the corner fitting and then rotated. Only after this rotation is the upper, still free crossbar aligned correctly, so that it can engage into the corner fitting of the upper container.
If such a twistlock is used the wrong way round by mistake, that is to say with the pivotable crossbar towards the bottom, the upward-directed anchoring foot of the housing would assume a position unsuitable for attaching the upper container. It would then be impossible for the corner fitting to be slipped over the twisted or skew anchoring foot. Consequently, errors are not possible with twistlocks of this type when containers are being loaded.
However, there still remains the above-described disadvantage of the relatively low load-bearing capacity.